As circuit dimensions shrink the need for fine-line lithography becomes more critical and the requirements for planarizing topography becomes very severe. Major U.S. semiconductor companies are actively pursuing Chemical-Mechanical Polishing (CMP) as the planarization technique used in the sub-half micron generation of chips. CMP is used for planarizing bare silicon wafers, interlevel dielectrics, and other materials. CMP machines, such as the one shown in FIG. 1, use orbital, circular, lapping motions. The wafer 16 is held on a rotating carrier 18 while the face of the wafer 16 being polished is pressed against a resilient polishing pad 14 attached to a rotating platen disk 12. A slurry is used to chemically attack the wafer surface to make the surface more easily removed by mechanical abrasion. Pad conditioning is done by mechanical abrasion of the pads 14 in order to `renew` the surface. During the polishing process, particles removed from the surface of the wafer 16 become embedded in the pores of the polishing pad 14 and must be removed. Current techniques use a conditioning head 22 with abrasive diamond studs to mechanically abrade the pad 14 and remove particles. Conditioning arm 24 positions condition head 22 over polishing pad 14.
Current chemical-mechanical polishing tools are physically large machines. Because of the low throughput of single wafer tools, the trend is toward multiple wafer tools. Current multiple wafer tools simply increase the number of polishing heads to match the number of wafers polished per run. This requires enormously complex robot and wafer carrier assemblies and substantial floor space. Multiple wafer tools, polishing 2-6 wafers per run, require matching of the multiple polishing heads to achieve good wafer-to-wafer uniformity. Furthermore, because the platen is rotating and the center of the pad has zero velocity, the wafer must be kept off-center from the platen for good uniformity. Accordingly, the platen itself must be much larger than the wafers being polished. Multiple wafer tools are thus very space consuming and can weigh in excess of 3 tons (2,700 Kg).